In monolithic semiconductor intergrated circuit (IC) devices it has become common to include lateral PNP transistors along with NPN vertical transistors in bipolar device circuits. Typically when high power dissipation is a requirement large area NPN transistors are employed. In many cases a large area collector is used to confront a plurality of separate emitters with interdigitated base electrodes. Finger electrodes are usually used to contact the individual emitters and these may include resistive sections that act as emitter degeneration resistors, ensuring that the total current is properly distributed among the various elements. One very common IC device is the voltage regulator in which the pass transistor is the main power dissipating element. When a positive voltage is being regulated the collector of the NPN pass transistor is connected to the input terminal. This means that the minimum voltage drop available is in excess of a transistor V.sub.BE. If a Darlington connection is used the limit is 2 V.sub.BE. However, if a PNP pass transistor is used the emitter is connected to the input terminal and the drop can be lowered to one V.sub.SAT which is normally considerably lower than V.sub.BE.
Another problem associated with the NPN positive voltage regulator is related to the IC version. As stated above the input terminal is connected to the collector of the pass transistor. In IC construction this would be a PN junction isolated region of substantial area. If such a device is inadvertently connected to a supply in the wrong polarity the isolation diode is forward biased. If the supply exceeds about 0.6 volt very heavy current can flow and destroy the IC. However, when the pass transistor is a PNP, the base represents the isolated region. If the P type emitter is connected to the wrong polarity supply, it becomes a reverse biased diode and no excess current will flow.
If a lateral transistor is to be constructed to have a high current gain, or Beta, it should have a large perimeter to area ratio. This requirement is satisfied by a relatively small circular emitter surrounded by a collector. When such a structure is to be employed in a device that is to be used for high power operation a large number of separate parallel connected devices will be needed. It is also clear that the base currents must be ballasted to overcome the natural tendency of such parallel connected structures to hog current. With a large number of elements the problem arises as to how the parallel connections are to be created along with the base current ballasting resistors. Thus far these problems have proven to be so formidable that high power PNP transistors have not been used to an appreciable extent, in IC's even though their availability is desired.